A typical dispensing device for supplying liquid, such as hot melt adhesive, generally includes a body having a valve that opens and closes a dispensing orifice. The valve is usually operated by pressurized air to dispense discrete amounts of pressurized liquid. One or more liquid seals within the device prevent the migration of liquid between the liquid and air passages of the device.
Devices generally related to the present invention include a liquid passage adjacent the dispensing orifice and an air passage or chamber at an opposite end of the device. The air passage contains a piston connected to a valve stem or pin on one side and may include a spring on the other side. Under sufficient air pressure, the piston and valve stem or pin may be moved in a direction away from the valve seat to discharge liquid. When the air pressure on one side of the piston is relieved, the spring will automatically return the pin to a normally closed position against the valve seat. Air pressure may also be used to close the valve stem or pin. The spring generally includes an adjustment to vary its compression and thereby vary the amount of air pressure required to open the valve. Adjustment of the spring compression will also adjust the biasing force used to close the valve. These devices may also include a stroke adjustment, or the spring adjustment may also vary the stroke of the valve stem or pin to adjust the flow rate.
Despite the wide success of devices as described above, continuing problems exist. For example, devices or modules of the same design may have various stroke lengths simply due to the stack up of internal parts which each have a range of dimensional tolerances. In addition, the valve stem or pin may be insufficiently supported against sideward movement and this may lead to increased wear of the various seals used around the pin. Existing dispensers have also required machining from both ends of the dispenser body. For this reason, different machining setups are required to form the same dispenser body. This leads to the potential for inaccurate alignment of the various bores and parts within the dispenser body. The number of parts required to assemble past dispenser modules or devices has also been relatively high and this increases parts and manufacturing costs. Finally, typical modules have included a rigidly connected or integrally formed flange on the end of the pin bearing against the return spring. This increases the possibility that side load is exerted on the pin by the spring and, again, this may lead to increased seal wear.
It would therefore be desirable to provide a dispenser module or device that may be readily substituted within applications currently utilizing existing dispensing devices or modules, but having various improvements eliminating or reducing problems such as those mentioned above.